The spring modules project build system is based on Ant and Ivy, and it's really interesting to have a look at how a modularized project can take advantage of advanced Ant and Ivy features to make the build simpler.

The webwork project (which should become struts action framework) uses ant+ivy for their build, and thus makes their framework very easy to use in an ant+ivy build system. They have a page documenting how to use Ivy with their framework, which can be an interesting reading, even if you don't plan to use webwork.